Yes, you can usually convert a Phoenix garage into an ADU. The city's guidance adds one condition many owners miss: when a garage or carport becomes living space, new off-street parking must be provided elsewhere on the lot, on a dustproof surface, and not inside the front yard setback.
Why does Phoenix ask for replacement parking?
Arizona law says a city cannot require additional parking to accommodate an ADU. Phoenix reads the garage as parking for the main house, so converting it means that parking has to move, not that the ADU needs its own space. As of October 2026, the City of Phoenix Beginner's Guide to ADUs states the replacement rule directly. Tempe's 2024 proposal took the same approach. We look for a legal spot for the new pad during the lot check, because a lot without one can rule the conversion out.
What work does a Valley garage usually need?
- Insulation. Most garages have little or none, and summer heat makes this the first priority.
- The door opening. The big garage door becomes framed wall with windows or an entry door.
- The slab. Garage floors often slope toward the door; leveling and a moisture barrier come first.
- Cooling. A ductless mini-split or a separate system sized for the room.
- Plumbing. A bathroom, and a kitchen if you want one, need drain lines cut through the slab.
- Electrical. A load calculation; many homes need a panel upgrade to carry the new unit.
Does a conversion follow the same size cap?
The Phoenix ADU caps still apply, but in practice the garage footprint is the limit. A typical two-car garage is well under the 1,000 sq ft cap for lots up to 10,000 sq ft, and the 75% of main-home rule rarely bites on a conversion.
What if the garage was never permitted?
Phoenix asks owners to legalize unpermitted structures before applying for an ADU permit. The city routes those cases through its Planning and Development ombudsman. We check permit history at the start so it does not surprise you halfway through design.
What does a conversion cost?
A Phoenix-area builder's July 2026 pricing puts a roughly 300 sq ft conversion with a kitchenette and three-quarter bath near $165,000, and its range for conversions and small attached units at $150,000 to $250,000. Other estimates run lower for simple rooms. Treat these as third-party figures; we price your garage after seeing it. See the Phoenix cost guide.